The instant invention is in the field of nanocomposite polymers. More specifically, the instant invention is in the field of compositions useful to make nanocomposite polymers and methods of preparing such compositions.
Delaminated or exfoliated cation exchanging layered materials (such as delaminated 2:1 layered silicate clays) can be used as reinforcing filler in a polymer system. Such polymer systems are known as “nanocomposites” when at least one dimension of the filler is less than two hundred nanometers. Nanocomposite polymers generally have enhanced mechanical property characteristics vs. conventionally filled polymers. For example, nanocomposite polymers can provide both increased modulus, lower density, improved clarity, lower coefficient of thermal expansion and in some instances increased impact toughness, a combination of mechanical properties that is not usually obtained using conventional fillers such as talc.
Transmission electron photomicrographs of nanocomposite polymers having a cation exchanging layered material filler typically show a dispersion of multiple layer units (e.g., from one to five layers per unit) of the cation-exchanging layered material in the polymer matrix. However, it is generally desired to achieve a high degree of delamination of the cation-exchanging layered material. Ideally the degree of such delamination is so extensive that only single layer units of the cation-exchanging layered material are present. If the cation-exchanging layered material is not sufficiently delaminated, then the mechanical property improvement of the polymer composite will usually be no better than if conventional micron sized filler is dispersed in the polymer.
Cation exchanging layered materials are often treated with an organic cation (usually an “onium”) as an “intercalation agent” to facilitate delamination of the cation exchanging layered material before the cation exchanging layered material is blended with a polymer (see, for example U.S. Pat. No. 5,973,053). However, the use of such intercalation agents increases the cost of the nanocomposite polymer and can act as a plasticizer for the polymer and thereby limit the strength, thermal resistance and stability of the nanocomposite polymer. It would be an advance in the nanocomposite polymer art if the use of such intercalation agents could be eliminated while never-the-less maintaining a sufficient degree of delamination of a cation exchanging layered material to produce a lower cost nanocomposite polymer having a better balance of physical property improvements.